I would very much like a reference on Louise FitzHugh's supposed pseudonym and her haunted paintings.
One thing I can tell you is, "Louise FitzHugh," the name under which she wrote *Harriet the Spy,* *Suzuki Beane,* etc., was *not* a pseudonym, as her father was named FitzHugh.
(Go here
http://www.purple-socks.com/regard.htm for biographical and critical information.) However, the paintings described in the *Village Voice* article sound plenty disturbing! You can tell by looking at her illustrations that she was more interested in revealing character and interior states through line than in photorealism or beauty in her art, which is a good starting point for creating creepy effects, but I can find no reference to a pseudonym anywhere.
I wonder if you're not conflating FitzHugh with another author - and if so, who that would be. I'm not doubting your truthfulness here, merely your memory. I confabulate out the wazoo myself, and I've seen authors conflated before. (I once met someone who insisted that P.L. Travers and Anne McCaffery were the same person, but was coy about his source; since both authors are tolerably well-documented this is, shall we say, unlikely.)
Certainly there's a visceral appeal to the notion of the author whose climactic life advice in her most famous work is "Sometimes you have to lie, but you should never lie to yourself" leading a double life; and to a certain extent, like most homoerotic people of her time period, she did. But the pseudonymous artist who is hidden by those administering her estate sounds like a fantasy persona to me.